Process of making reinforced hollow slabs



W. H. COBI April 11, 1939.

PROCESS OF MAKING REINFORcEIS HOLLOW SLABS Filed Dec. 14. 1936 2 Sheets-Sheet l INVENTOR I April 11, 1939. w co 2,153,741 7 PROCESS OF MAKING REINFORCED HOLLOW SLABS Filed Dec. 14, 1936 2 Sheets-Sheet 2 l INVENTOR iii Patented Apr. n, 193a UNITED STATES PATENT orrics PROCESS OF MAKING RWRCED HOLLOW SLABfi Walter Gobi, New ii'orh, N. ll. Application December in, race. Serial No. 115,729

5 Claims.

This invention relates to hollow concrete blocks and slabs and has for its object to provide an improved process andappar atus for making such slabs, as well as to provide an improvedslab of this type.

It is known that concretein setting exerts a binding action upon a core or the like which may be placed therein; While hollow beams or slabs are desirable for numerous purposes there have been no commercial satisfactory ways of forming such hollow slabs where they are considerably longer than ordinary building blocks. This is believed to be due to the difficulty in extracting a core. In making short concrete blocks one expedient has been to use a relatively dry cementitious material which can hold its shape immediately after being compressed so that the core may be withdrawn without waiting for the ma-= terial to set. A variety of collapsible cores have been suggested but a dimculty with many of these has been the sticking of the core to the cementitious material and the difilculty in loosening them.

According to this invention these dihlculties have been eliminated by loosening the cores from the set concrete, by sequentially prying the cores loose and by prestressing the hollow slab when set.

Referring to the drawings- Fig. l is a side elevation partly in section showing the apparatus for making hollow concrete slabs.

Fig. 2 is an exploded view of the end wall of the mold and the tensioning apparatus.

Fig. 3 is a longitudinal view partly in section through the collapsible core.

Fig. 4 is a section on the line 5-4 of Fig. 3.

. Fig. 515 a perspective illustrating the way in which the collapsible core is ,removed from the cast slab.

Fig. 6 is a perspective showing one type of concrete slab made by this invention. In Fig. 1 the concrete block or slab l is'formed in the mold illustrated which iscomprised of a bottom. portion H, side walls not shown and an end wall l2. To the bottom or the mold may be attached some usual type of vibrating mechanism such as is customarily used with molds. The reinforcing means is extends through the upper and lower portions of the slab and as shown in Figs. 1 and 2 the longitudinal reinforcing members extend through the end wall I 2 where they may be attached to clamps H for the purpose of applying stress to these tension means and holding them under stress while the cementitlous material is setting. The gripping means it which hold the ends ofthe reinforcing wires may be tightened by means of rotation of the spindles shown so that stress is transmitted from the reinforcing wires lil to the frame it and to the end wall iii of the mold.

The inner face of the end Wall i2 includes a rubber or other yieldable material l l for the purpose of engaging the end of the core i9 and also for the purpose of forming a snug fit around the 10 reinforcing wires where they pass through the end wall. As shown in Fig. 2 the end wall is made in at least three portions, a main or middle portion grooved to receive the reinforcing wires and end or capping portions for closing the grooves through which the reinforcing wires pass.

Secured to the end wall is-a center clip 53 comprising spring fingers adapted to engage the inner end walls of the core to assist in centering or positioningthe core within the mold. A similar end wall may be used at the other end of the f mold, but instead of using clamps and other tensioning means for the reinforcement it will be understood that the reinforcing wires may be seecured to a fixed support whereby the tensioning means is necessary at only one end of the mold. The end walls of the mold may clamp the core between them and thus assist in supporting the core during the molding process. The engagement between the ends of the core and the rub- 0 her or other yieldable material ll provides a substantially liquid-tight seal to keep the cementitious material from getting inside of the core during pouring or setting.

As shown in Figs. 3, 4 and 5 the collapsible core includes comparatively thick. wall portions 20 connected by much thinner portions 29 which are soldered or otherwise secured to the thick walls.

In practice. it has been found desirable to make the thick walls of about ,6 inch commercial sheet tin whiletthe thin walls 2| may be of brass only about .065 inch thick. For expanding the collapsible core there is provided a fluid pressure holder 22 which is of pure gum rubber about-541 inch thiclr'and constructed to withstand an internal air pressure of forty. to fifty pounds per square inch. The fluid pressure holder 22 contacts with a series of blocks 23 which press, outwardly upon'the thick walls of the core. Within the rubber container 22 is a tension rod 24 arranged to prevent the end plugs 25 from pulling out under the internal pressure. The 'plugs 25 may be vulcanized or securely cemented to the walls of the pressure holder and end rings 26 Y The left end of the core in Fig. 3 is shown as being provided with an ordinary valve stem such asisusedintires andthroughthisrodl'l the inflating and deflating operations may take place.

Eyes 2| or the equivalent are secured to the inside of the core adjacent one end so that the ends of a gripping handle may be engaged and assist in withdrawing the core from the finished slab. Fig. 2 shows how the springs of the centering clip I! are slotted at to give clearance for the eyes 20.

In operation the bottom of the mold is generally made of ply wood and substantially wider than the mold so that the sides may, if desired, rest upon it. The desired tension, about 3000 to 5000 pounds per square inch is maintained on the reinforcing wires I! while the concrete is setting. After it has set the external tension applying means is disconnected from the reinforcing wires with the result that the portions of the concrete around these wires are placed under an initial compression while the reinforcing wires still remain under tension. The compression initially placed on the slabs not only strengthens them and makes them better adapted for use as beams but the initial stressing of the concrete on removing the tension applying means from the reinforcing members also assists in releasing the core from the gripping action in which it is held by the concrete in setting, due to a shortening of the slab. The core itself when expanded in position may have substantial compression placed upon it by the end walls, although if desired this is not necessary since the pressure on the end walls may be transmitted to the side walls of the mold without passing through the core to any substantial extent.

It is thought, however, that stressing the core in this manner may assist in releasing the core from the gripping action of the concrete and allow a small displacement to occur between the concrete and core when any longitudinal compression is removed from the core and placed upon the concrete. .After removal of the end walls and deflating the fluid pressure holder, it may be necessary to drive a wedge between each thick side of the core and the contiguous concrete for the purpose of sequentially loosening the core from the concrete and allowing the core to be contracted radially inward.

In separating the sides 20 from the concrete the thin sides 2i are also disconnected from the concrete. After collapsing the core may be again inflated and inserted in position for use over a ain.

.Among the advantages of this invention may be mentioned'the simplicity and ease'with which the collapsible core may be The prestressing of the concrete is believed to assist in removal of the core. Where'the'term" concrete has been used a more precise term should be cement mortar or grout. Inpouringwthecementitlous material is preferably of a creamy consistency and not the .liquid. A cover may be used on the mold if cementitious material is preferably one part of cement to two or three parts of sand. The hollow beams being under an initial compression are better adapted to withstand flexure than would be the case if they did not have such initial compression.

As used herein the term "slab signifies an elongated block whether used as a beam or column.

I claim:

1. ,The process of making a reinforced hollow slab of moldable material which comprises longitudinally tensioning the reinforcements of said slab while simultaneously longitudinally compressing a core within said slab during setting of the material and then prestressing the slab when set from the stress in said reinforcements to facilitate removal of said core.

2. The process of making a reinforced hollow slab of moldable material which comprises longitudinally tensioning the reinforcements of said slab while simultaneously longitudinally compressing a collapsible core containing internal pressure within said slab during setting of the material and then prestressing the slab when set from the stress in said reinforcements and core and removing the internal pressure from said core to facilitate its removal.

3. The process of assisting in the removal of a core from a reinforced hollow slab of moldable material which comprises externally and longitudinally tensioning the reinforcing means of said slab and simultaneously externally stressing said core longitudinally under compression while the moldable material is setting, and after material which comprises externally and longitudinally tensioning the reinforcing means of said slab and simultaneously externally stressing said core longitudinally under compression and transversely under tension while the moldable material is setting, and after the material has set removing the external longitudinal and the internal transverse stress from said core and the external tension from said reinforcing means whereby said slab is placed under an initial compression and the core tends to become loosened from the set slab material.

5. A process of making a reinforced hollow slab from plastic cementitious material which comprises applying a longitudinal tensioning force to the reinforcement elements embedded within said material and simultaneously applymg a longitudinally compressive force tora re- 'IWAL'I'ER rrconr. 

